Cadmium in Mytilus spp.: Worldwide survey and relationship between seawater and mussel content

A worldwide literature survey of data on cadmium concentration in the soft tissue of the mussel, Mytilus spp., from 591 stations is presented. These stations are from 13 regions. Geometric means for the regions vary from 0·6 to 3·3 μg g⁻¹ (dry weight) for the Barents Sea and the Northeastern Pacific coast, respectively.The averages of seven of these regions, for which reliable cadmium concentrations in seawater were available, were used to calculate a relationship between cadmium concentrations in seawater and mussel soft tissue. The relationship was highly significant: (Cd) mussel (μg g⁻¹, dry weight) = 0·074 (Cd) water (ng litre⁻¹) + 0·39 (P ≤ 0·0005).This model has been successfully applied in the context of the contamination of the Gironde estuary (France). It can also be used to define a water quality criterion for mussel maturing parks consistent with the quality criterion defined for shellfish for human consumption.     

The solubility of calcite in seawater at atmospheric pressure and 35%permil; salinity

The apparent (stoichiometric) solubility product of calcite in artificial seawater of salinity 35‰ was measured by a saturometer technique. The value of the apparent solubility product was found to be (4·59 ± 0·05) × 10⁻⁷ moles/(kilogram of seawater)² at 25°C with a temperature coefficient of −0·0108 × 10⁻⁷/°C between 2 and 25°C. These values are significantly smaller than those found by MacIntyre (1965) and other workers. The effect of these results on the saturation of the oceans with respect to calcite is examined.     

The distribution and population dynamics of O-group plaice (Pleuronectes platessa L.) on nursery grounds in the Firth of Forth

Midsummer (1 August) population estimates of about 2 million O-group plaice (Pleuronectes platessa L.) were derived for sandy bays around the Firth of Forth in 1979–1980. This is an order of magnitude less than similar estimates made for the Clyde Sea Area in 1973–1974. Autumn population estimates of 0·4–1·0 million fish were comparable to estimates by the Ministry of Agriculture, Fisheries and Food for the area between the Scottish border and Flamborough Head (2·3 million for 1970 and 1973) which represented 4·8% (1973) to 5·3% (1970) of the total number of O-group fish on the English east coast.Largo Bay was the most important nursery area holding 25% of the total population. It is particularly well situated to receive newly metamorphosed plaice carried in water currents along the north side of the Forth from the spawning ground off Fife Ness. Plaice in the Forth are mainly distributed on fine to medium sandy beaches (186–480 μm), the mean number per haul in midsummer (D) being correlated with the median diameter (m.d. in μm) of the low water sediments by the equation: D=−45·7666+0·2327 m.d. (n=11,r=0·68,P<0·02 but>0·01).The shallow inshore water in sandy bays in the outer Firth was well mixed and more marine than estuarine (27·7–35·0‰). The correlation coefficient between fish density and water temperature was low, while that with salinity (S‰) was: D=6·1618+0·2238S (n=23,r=0·62,P<0·005).Regression analysis demonstrated that the relationship between the instantaneous mortality rate (Z) and the initial population density (D_p) was: Z×100=0·7480+0·0546d_p (n=12,r=0·87,P<0·001).The mean mortality rate for the O-group plaice in the Forth nursery areas was 53% month⁻¹.     

Solubility of calcite in the ocean

The apparent solubility product K′_sp of calcite in seawater was measured as a function of temperature, salinity, and pressure using potentiometric saturometry techniques. The temperature effect was hardly discernible experimentally. The value of K′_sp at 25°C was 4.59·10⁻⁷ mole²/(kg seawater)² at 35‰S, 5.34·10⁻⁷ at 43‰S, and 3.24·10⁻⁷ at 27‰S. The apparent partial molal volume was found to be −34.4 cm³ at 25°C and −42.3 cm³ at 2°C from a linear fit of log(K′_sp ^P/K′_sp ¹). These results were used in conjunction with field data to calculate the degree of saturation in the oceans and showed undersaturation at shallower depths than previously reported.     

Differences in the effects of mercury on predator avoidance in two populations of the grass shrimp Palaemonetes pugio

Adult Palaemonetes pugio were collected from two tidal creek systems, Piles Creek (PC), a mercury polluted estuary, and Big Sheepshead Creek (BSC), a relatively pristine creek. Adult killifish (Fundulus heteroclitus), a natural predator of P. pugio, were obtained from BSC. For each test, ten treated (0·01 mg/liter mercuric chloride (HgCl), or 0·01 mg/liter methylmercuric chloride (MeHg)), or control shrimp here introduced into a tank containing three fish. The time between capture of the first and second BSC HgCl treated shrimp was significantly faster (P < 0·05), as was the time between the first and second capture (P < 0·05) of MeHg treated BSC shrimp when compared with their respective controls. In addition, significantly more (P < 0·025) BSC HgCl treated shrimp were captured after 120 min. No significant difference existed between control and HgCl treated PC shrimp; however, significantly more PC MeHg treated shrimp were captured after 60 (P < 0·05) min when compared with their respective controls. These data suggest that PC shrimp, subjected to mercury in their natural environment, are more tolerant to the sublethal effects of both HgCl and MeHg. These data also suggest that behavioral studies can be very sensitive assays for determining the effects of sublethal concentrations of toxicants on populations of organisms.     

Induction of heat shock protein (hsp)60 in Isochrysis galbana exposed to sublethal preparations of dispersant and Prudhoe Bay crude oil

Adaptation to sublethal exposure to crude oil by phytoplankton is poorly understood. Use of chemical dispersants for oil spill remediation increases petroleum hydrocarbon concentrations in water, while exposing marine organisms to potentially toxic concentrations of dispersant. Heat shock proteins (hsps) have been found to serve as an adaptive and protective mechanism against environmental stresses. The objective of this project was to examine the induction of hsps in Isochrysis galbana, a golden-brown algae, following exposure to the water-accommodated fraction (WAF) of Prudhoe Bay crude oil (PBCO) and PBCO chemically dispersed with Corexit 9527® (dispersed oil: DO). Initial experiments using ³⁵S-labeled amino acids and 2-dimensional electrophoresis with subsequent western blotting identified and confirmed hsp60, a member of the chaperonin family of stress proteins, as being efficiently induced by heat shock in this species. One-dimensional SDS PAGE and western blotting, with hsp60 antibodies and chemiluminesence detection, were used to quantitate hsp60 following exposure to a range of environmental temperatures and concentrations of WAF and DO preparations. I. galbana cultured in 22 parts per thousand (‰) salinity showed a statistically significant increase (p<0.05) in hsp60 after exposure to 25, 30, and 35°C for 1 h compared to controls (20°C), while 34‰ cultures showed no significant increase in hsp60 with increasing temperature. Cultures (22 and 34‰) exposed to varying doses of WAF and DO exhibited statistically significant (p<0.05) increases in levels of hsp60 in all cases. A dose-related response was observed in all exposures (r²≥0.90) with the exception of 34‰ WAF. In independent exposures, a dose-related hsp60 response to naphthalene, a relatively abundant water-soluble aromatic hydrocarbon, was observed in both 22 and 34‰ cultures. Results of this study are consistent with previous studies in other species documenting increases in hsp60 levels with exposure to xenobiotics. Further studies are investigating the protective function of hsp60 against the toxic effects of exposure to WAF and DO preparations.     

Nutrient flux in the Rhode River: Tidal transport of microorganisms in brackish marshes

Concentrations of bacteria, chlorophyll a, and several dissolved organic compounds were determined during 11 tidal cycles throughout the year in a high and a low elevation marsh of a brackish tidal estuary. Mean bacterial concentrations were slightly higher in flooding (7·1 × 10⁶ cells ml⁻¹) than in ebbing waters (6·5 × 10⁶ cells ml⁻¹), and there were no differences between marshes. Mean chlorophyll a concentrations were 36·7 μg l⁻¹ in the low marsh and 20·4 μg l⁻¹ in the high marsh. Flux calculations, based on tidal records and measured concentrations, suggested a small net import of bacterial and algal biomass into both marshes. Over the course of individual tidal cycles, concentrations of all parameters were variable and not related to tidal stage. Heterotrophic activity measured by the uptake of ³H-thymidine, was found predominantly in the smallest particle size fractions (< 1·0 μm). Thymidine uptake was correlated with temperature (r = 0·48, P < 0·01), and bacterial productivity was estimated to be 7 to 42 μg Cl⁻¹ day⁻¹.     

The solubility of CaCO3 in seawater at 2°C based upon in-situ sampled pore water composition

Analyses of the concentration product (Ca²⁺) × (CO₃²⁻) in the pore waters of marine sediments have been used to estimate the apparent solubility products of sedimentary calcite (K′_SPc) and aragonite (K′_SPa) in seawater. Regression of the data gives the relation In K′^P_SPc = 1.94 × 10⁻³ δP − 14.59 The 2°C, 1 atm value of K′_SPc is, then, 4.61 × 10⁻⁷ mol² l⁻². The pressure coefficient yields a at 2°C of −43.8 cm³ atm⁻¹. A single station where aragonite is present in the sediments gives a value of K′_SPa = 9.2 × 10⁻⁷ (4°C, 81 atm). The calcite data are very similar to those determined experimentally by Ingle et al. (1973) for K′_SPc at 2°C and 1 atm. The calculated is also indistinguishable from the experimental results of Ingle (1975) if is assumed to be independent of pressure.     

Measurement of manganese, zinc and cadmium complexation in seawater using Chelex ion exchange equilibria

Equilibria between Chelex 100* and manganese, zinc and cadmium ions were used to determine the complexation of these trace metals in 36‰ Gulf Stream seawater at 25°C and pH 8.2. The method utilized radiotracers (⁵⁴Mn, ⁶⁵Zn, and ¹⁰⁹Cd) to quantify trace metal adsorption from trace metal-amended seawater and from seawater containing a series of ethylenediaminetetracetate (EDTA)—metal ion buffers. Results were consistent with Chelex adsorption of both trace metal ions and trace metal—EDTA chelates. Equilibrium models fitted to the data were used to establish conditional stability constants for Chelex adsorption of manganese, zinc and cadmium ions and for adsorption of EDTA-chelates. These models also yielded ratios of free metal ions to total dissolved trace metal concentrations in seawater: 10^−0.1 for manganese, 10^−0.2 for zinc, and 10^−1.5 for cadmium. Independent measurements with a cadmium ion-selective electrode also yielded a free: total cadmium ratio of 10^−1.5.     

Impact of environmental factors on in situ determination of iron in seawater by flow injection analysis

A sensitive method for iron determination in seawater has been adapted on a submersible chemical analyser for in situ measurements. The technique is based on flow injection analysis (FIA) coupled with spectrophotometric detection. When direct injection of seawater was used, the detection limit was 1.6 nM, and the precision 7%, for a triplicate injection of a 4 nM standard. At low iron concentrations, on line preconcentration using a column filled with 8-hydroxyquinoline (8HQ) resin was used. The detection limit was 0.15 nM (time of preconcentration = 240 s), and the precision 6%, for a triplicate determination of a 1 nM standard, allowing the determination of Fe in most of the oceanic regimes, except the most depleted surface waters. The effect of temperature, pressure, salinity, copper, manganese, and iron speciation on the response of the analyser was investigated. The slope of the calibration curves followed a linear relation as a function of pressure (C_p = 2.8 × 10^{− 5}P + 3.4 × 10^{− 2} s nmol^{− 1}, R² = 0.997, for Θ = 13 °C) and an exponential relation as a function of temperature (C_Θ = 0.009e^0.103Θ, R² = 0.832, for P = 3 bar). No statistical difference at 95% confidence level was observed for samples of different salinities (S = 0, 20, 35). Only very high concentration of copper (1000 × [Fe]) produced a detectable interference. The chemical analyser was deployed in the coastal environment of the Bay of Brest to investigate the effect of iron speciation on the response of the analyser. Direct injection was used and seawater samples were acidified on line for 80 s. Dissolved iron (DFe, filtered seawater (0.4 μm), acidified and stored at pH 1.8) corresponded to 29 ± 4% of Fe_a (unfiltered seawater, acidified in line at pH 1.8 for 80 s). Most of Fe_a (71 ± 4%) was probably a fraction of total dissolvable iron (TDFe, unfiltered seawater, acidified and stored at pH 1.8).     

Trace metal fronts in Scottish coastal waters

Dissolved cadmium and copper concentrations have been determined in 76 surface water samples in coastal and ocean waters around Scotland by anodic stripping voltammetry (ASV). A trace metal/salinity ‘front’ is observed to the west, north and north-east of Scotland separating high salinity ocean water (>35 × 10⁻³) with low concentrations of dissolved Cd and Cu from lower salinity (<35 × 10⁻³) coastal water containing higher concentrations of Cd and Cu. Mean Cd concentrations in ocean and coastal waters are 7 ng dm⁻³ (0·06 n ) and 11 ng dm⁻³ (0·10 n ) respectively; for Cu the respective levels are 60 ng dm⁻³ (0·95 n ) and 170 ng dm⁻³ (2·68 n ). The observed distribution is attributed principally to freshwater runoff and the advection of contaminated Irish Sea water into the study area.     

The effect of cadmium on some oxygen-binding properties of the blood pigment of the lugworm Arenicola marina (annelida, polychaeta)

The effect of cadmium was determined on some oxygen-binding characteristics (viz. oxygen affinity, subunit cooperativity, Bohr-effect and temperature effect) of the erythrocruorin of the lugworm, Arenicola marina.Oxygen affinity and subunit cooperativity were measured directly in the blood of Arenicola, both in blood collected from specimens kept under experimental conditions and from specimens obtained from their natural habitat.In the pH range of 7·3–7·8, which closely resembles in vivo blood pH values, cadmium does not affect the oxygen affinity at low concentrations (10⁻⁸-10⁻⁵ ), and decreases the O₂-affinity only slightly at higher concentrations (10⁻⁵-2·10⁻³ ). In the more alkaline pH range, the oxygen affinity increases considerably with increasing cadmium concentrations.Cadmium exerts a facilitating influence on the haem cooperativity at lowest concentrations (10⁻⁸-10⁻⁷ ) and a minor inhibiting influence at higher concentrations.The oxygen affinity, subunit cooperativity, the Bohr-effect and the temperature effect are pH dependent.The influence of cadmium on the magnitude of the Bohr-effect is pH-dependent.In vivo measurement of the oxygen affinity of Arenicola erythrocruorin gives evidence of a more pronounced inhibition of oxygen binding at increasing cadmium concentrations in the blood, compared with the effect on purified erythrocruorin solutions.     

Study of fluoride in polluted and unpolluted estuarine environments

Mindhola River estuary, which receives industrial waste containing high concentrations of fluoride, and Purna River estuary, which is free from fluoride contamination, have been investigated. While fluoride behaved conservatively in Purna River estuary, significant deviation from the theoretical dilution line (TDL) in the chlorinity range 0·5–8‰ was observed in Mindhola River estuary due to the externally added fluoride which largely remained in solution. The excess of fluroide over the theoretically calculated value was at a maximum around a chlorinity of 3‰. High natural fluoride content of the river waters resulted in F/Cl ratios exceeding 300 × 10⁻⁵ at low chlorinities. The ratio decreased rapidly with increasing chlorinity and the value near to that of seawater was observed at chlorinities above 14‰.     

Interaction of cadmium and copper with surface-active organic matter and complexing ligands released by marine phytoplankton

The organic matter released by the marine phytoplankton species Dunaliella tertiolecta and its physico-chemical interaction with cadmium and copper ions were studied by electrochemical methods (differential pulse anodic stripping voltammetry (DPASV) and a.c. polarography). The interactions with cadmium and copper were studied at the model interface (mercury electrodesolution) and in the bulk phase by measuring the complexing ability of the released organic material.The axenic cultures were grown on different growth media, without and with trace metals and chelators. Culture media were analyzed 10 days after inoculation, containing 5 × 10⁵−1.2 × 10⁶ cells cm⁻³ when untreated or after separation of cells by gentle centrifugation.It was found that the content and type of the released surface-active material and complexing ligands depend on the initial composition of the growth media. In all cases, strong interaction of excreted organic substances with copper in the bulk phase and with cadmium at the model interface were observed.A rather high value of the complexing capacity, 9.5 × 10⁻⁷ mol Cu²⁺ dm⁻³, was found in the culture grown on medium without trace metals and chelators (medium I) whereas the surface activity of this culture was not high (0.2 mg dm⁻³ equivalent to Triton-X-100). Higher contents of surface-active material (0.8 and 1.0 mg dm⁻³) were found in cultures grown in media with trace metals and without chelators (II and III), accompanied by a high content of complexing ligands (5.8 × 10⁻⁷ and 9.5 × 10⁻⁷ mol Cu²⁺ dm⁻³). However, if the complexing capacity is calculated per cell the values obtained for cultures grown in media II and III (0.79 × 10⁻¹⁵ and 0.98 × 10⁻¹⁵ mol Cu²⁺ dm⁻³) are lower than for cultures grown on medium I (1.8 × 10⁻¹⁵ mol Cu²⁻ dm⁻³). The exceptional adsorption effects and the copper complexing capacity for medium 1, and the presence of cells with degenerative symptoms can be ascribed to stressed growth conditions, and, particularly, to deficiency of metals. A qualitatively similar behaviour has been observed in natural samples of estuarine waters, indicating the existence of stressed conditions during the mixing of fresh and saline waters.     

Evidence for microbiological manganese oxidation in the river Tamar Estuary, South West England

Water samples from the Tamar Estuary oxidized manganese when supplemented with Mn²⁺ (2 mgl⁻¹). The rates of oxidation were depressed in the presence of various metabolic inhibitors. The effect of Mn²⁺ and temperature on the rate of manganese oxidation suggested that a biological process was largely responsible for converting Mn²⁺ to Mn⁴⁺. Rates of manganese oxidation were much higher in freshwater (3·32 μgl⁻¹ h⁻¹ in water containing 30 mgl⁻¹ of suspended matter) than in saline water (0·7 μgl⁻¹ h⁻¹ in water of salinity 32‰) containing the same amount of particulate matter. The rate of manganese oxidation was proportional to the particulate load (up to 100 mgl⁻¹ particulates).     

Carbon and nitrogen stable isotopes in suspended matter and sediments from the Schelde Estuary

The C/N and stable C and N isotope ratios (δ¹³C, δ¹⁵N) of sedimentary and suspended particulate matter were determined in the Schelde Estuary. Suspended matter was divided into 2 to 5 size fractions by centrifugation. Four major pools of organic matter were recognized: riverine, estuarine, marine and terrestrial materials. Terrestrial organic matter (δ¹³C≈−26‰, δ¹⁵N≈3.5‰, C/N≈21) is important for the sedimentary pool, but suspended matter is dominated by the marine (δ¹³C≈−18‰, δ¹⁵N≈9‰, C/N≈8), riverine (δ¹³C≈−30‰, δ¹⁵N≈9‰, C/N≈7.5) and estuarine (δ¹³C≈−29‰, δ¹⁵N≈15‰, C/N≈8) end-members. In the upper estuary, the suspended matter size fractions vary systematically in their carbon and nitrogen biogeochemistry, with the small particles having low C/N ratios, depleted δ¹³C and enriched δ¹⁵N values relative to large particles. Moreover, sedimentary and suspended matter differ significantly in terms of C/N ratios (17 vs. 8.9), δ¹³C (−26.3 vs. −28.9‰) and δ¹⁵N (+6.9 vs. 12.0‰). In the lower estuary, suspended matter fractions are similar and sedimentary and suspended organic matter differ only in terms of δ¹³C (−23.5 vs. −20.1‰). Our data indicate that autochthonous organic matter contributes significantly to the total suspended matter and that the suspended organic matter composition cannot be explained in terms of conservative mixing of riverine and terrestrial sources on the one hand and marine sources on the other hand.     

Association of picophytoplankton distribution with ENSO events in the equatorial Pacific between 145°E and 160°W

Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg⁻¹), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg⁻¹) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg⁻¹). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×10³ cells ml⁻¹, Synechococcus in the frontal zone with >15×10³ cells ml⁻¹, and picoeukaryotes in the upwelling region with >8×10³ cells ml⁻¹. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field.     

Determination of Henry's law constants for hexachlorocyclohexanes in distilled water and artificial seawater as a function of temperature

Henry's law constants were determined for α- and γ-hexachlorocyclohexane (HCH) as a function of temperature (0.5–45°C) in artificial seawater (SW; 30‰) and distilled water (DW) using the gas stripping method. Water samples (1–5 ml) were withdrawn from the stripping vessel during the stripping process (30–360 h), solvent extracted and analyzed by gas chromatography—electron-capture detection. The effect of bubbling depth was checked to ensure that bubbles leaving the system were at equilibrium with HCHs in the aqueous phase. Henry's law constants determined at 35 and 45°C in SW were significantly higher (P≤ 0.05) than in DW for both α- and γ-HCH, but not at lower temperatures. The slopes (m) and intercepts (b) of log H vs. 1 / T plots were: α-HCH (DW, 0.5–45°C); m = −2810 ± 110, B = 9.31 ± 0.38; α-HCH (SW, 0.5–23°C); M = −2969 ± 218, B = 9.88 ± 0.76; γ-HCH (DW, 0.5–45°C); M = −2382 ± 160, B = 7.54 ± 0.54; γ-HCH (SW, 0.5–23°C); M = −2703 ± 276, B = 8.68 ± 0.96. Henry's law constants determined in this study compared well with those calculated from reported vapor pressure and solubility data.     

Seasonal phytoplankton composition, productivity and biomass in the Neuse River estuary, North Carolina

Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m⁻², mean chlorophyll a was 11·8 mg m⁻³, and mean phytoplankton density was 1·56 × 10³ cells ml⁻¹. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m⁻².     

Relationships between macroalgal biomass and nutrient concentrations in a hypertrophic area of the Venice Lagoon

Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m⁻² day⁻¹, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m⁻² day⁻¹) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre⁻¹ for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre⁻¹ for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g⁻¹ for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m⁻³ as Chl. a, sharply increased up to 100 mg m⁻³ only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).